It is well known in the art that automatic dishwashers corrode glassware particularly when cleaned with highly alkaline detergent compositions. See Newton, R. G., The Durability of Glass-A Review, Glass Technology Vol. 26 No. 1, February 1985, pp. 21-38 and U.S. Pat. No. 4,933,101 (Cilley et al.). The visible forms of glassware corrosion are generally caused by hydrolysis and therefore dissolution of the glassware's silicate network. This dissolution is known to be very low at pH values below 9.5 and increases with increasing pH (see Kruger, A. A., The Role of the Surface on Bulk Physical Properties of Glasses, in Surface and Near-Surface Chemistry of Oxide Materials, eds. Nowotny, J., and Dufour, L.-C., pp. 413-448). Thus detergent compositions having an alkalinity of less than about pH 10 were conventionally believed to exert very low corrosivity towards glassware.
Cleaning restrictions forced prior art formulators to seek solutions to tableware corrosion while maintaining high alkalinity in detergent products. The art teaches that silicate in combination with fast dissolving aluminum salts avoids high alkalinity corrosion of glassware. See U.S. Pat. No. 3,350,318, issued on Oct. 31, 1967 to Green and U.S. Pat. No. 3,255,117 issued Jun. 7, 1966 to Knapp et al.
As detergent compositions have increasingly become based on enzymes allowing the products to be milder and more environmentally friendly, it was believed that glassware corrosion would not be a problem especially at pH values of less than about 10.
It has now been discovered that detergent formulations having neutral pH or low alkalinity significantly corrode fine tableware, particularly lead crystal glassware. It is believed that the lead and boron minerals of the tableware take part in the formation of the silicate network. When such minerals are extracted the silicate network falls apart readily. This corrosion is especially pronounced in the absence of silicate which is not always incorporated in low alkalinity or neutral pH products. It has further been observed that detergent compositions incorporating aluminum salts to inhibit corrosion compromise cleaning and leave significant stains on washed tableware.
It has been surprisingly discovered that by utilizing certain slow dissolving aluminum salts in automatic dishwashing compositions that tableware corrosion can be inhibited and that cleaning efficiency can be improved.
It has also been surprisingly discovered that by utilizing certain sequestrants in combination with any water soluble aluminum salt that both tableware corrosion and the negative impact on cleaning efficiency can be minimized.
It is thus an object of the present invention to provide improved pH-neutral to mildly alkaline automatic dishwashing detergent compositions which not only protect against tableware corrosion but also provide good cleaning performance in removing stains from tableware.
Another object of the invention is to provide a process for incorporating selected slow dissolving aluminum salts in an automatic dishwashing detergent composition to provide effective cleaning performance without tableware corrosion.